1. Field of the Invention
The present invention relates to a laminate-type ceramic electronic component, and in particular, to a laminate-type ceramic electronic component in which plural coils are magnetically-coupled to each other, such as a laminate-type common mode choke coil, a laminate-type transducer or other suitable component.
2. Description of the Related Art
Common mode choke coils have a structure in which the magnetic fields of two coils intensify each other to produce a magnetic material loss when common mode noise is applied. On the other hand, when a normal mode signal is applied, the magnetic fields of the two coils are cancelled out by each other so that no magnetic material loss is generated. In particular, when inductances generated by the two coils are equal, the magnetic field is minimal, and a minimum magnetic loss is generated for an applied normal mode signal. Thus, the common mode choke coils are designed so that the inductances of the two coils are equal.
According to a known common mode choke coil such as a laminate-type common mode choke coil described in Japanese Unexamined Patent Application Publication No. 2002-373809, two coils are arranged in the lamination direction of ceramic layers while the axial directions of the two coils substantially are set so as to coincide with the lamination direction of the ceramic layers. As shown in FIG. 7, a common mode choke coil 110 as described above includes ceramic sheets 132 having coil conductors 111 to 114 and 115 to 118, and via-holes 126 used for connection between layers, an interlayer ceramic sheet 133 having no conductor formed thereon, outer layer ceramic sheets 134, and so forth.
The coil conductors 111 to 114 are electrically connected in series through the interlayer connection via-holes 126 formed in the ceramic sheets 132 to form a spiral coil La. The coil conductors 115 to 118 are electrically connected in series through the interlayer connection via-holes 126 formed in the ceramic sheets 132 to form a spiral coil Lb.
The ceramic sheets 132 are laminated and integrally fired to form a laminate. Input-output external electrodes are formed on the surface of the laminate.
In the common mode choke coil 110, in some cases, the numbers of turns of the two spiral coils La and Lb can not be set to be equal, depending on the positions of their input-output external electrodes. The numbers of turns of the spiral coils La and Lb are compared below. The number of turns of the spiral coil Lb is larger than that of the spiral coil La by the sum of the lengths shown by surrounding ellipses A1 and A2 (total of about 0.5 turn) in FIG. 7, irrespective of the number of laminated ceramic sheets.
If the numbers of turns of the two spiral coils La and Lb are different, the difference between the numbers of turns will cause the difference between the inductances generated by the coils La and Lb (impedances). When the inductances (impedances) of the two coils La and Lb provided in the common mode choke coil 110 are unbalanced, a large inductance (impedance) is generated, and a dielectric material loss is generated for a normal mode signal applied.
According to the known common mode choke coil 110, the difference between the inductances of the two spiral coils La and Lb is adjusted by partially changing the sizes of the spiral coils La and Lb, the widths of the coil conductors 111 to 114 and 115 to 118, or the like.
However, in the case where the patterns of the coil conductors 111 to 114 and 115 to 118 are changed, the number of the types of patterns for the coil conductors 111 to 114 and 115 to 118 increases. It is difficult to manage the formation of such a large number of patterns. Moreover, to adjust the inductances in the above-described manner, it is necessary to prepare several types of patterns for trial and error adjustment.
If the patterns are changed, a change will be caused in a magnetic flux, depending on the types of the changed patterns. Thus, the magnetic coupling between the spiral coils La and Lb is undesirably deteriorated. That is, a dangerously low inductance will be generated when common mode noise is applied, and a large inductance will be generated for a normal mode signal applied.